Funds are requested to expand and improve the animal housing and support facilities at the Massachusetts General Hospital. A critical need has been identified to provide for barrier facilities to house chimeric rodents (mice) produced using Gene Replacement (Knockout) Technology and traditional transgenic mice. The barrier space has been provided through institutional funds. Funds are needed to properly equip these facilities. These funds will be used to purchase additional micro-isolator units and rodent racks, and replace deteriorated micro-isolator housing units and workbenches which do not meet the standards of the "Guide." The experimental transplantation program has experienced successes which require a redirection and expansion of the program to include a second non-human primate species (baboon) for xenographic studies. Appropriate cages for housing baboons are not available and must be obtained in order to allow continued research using large baboons. The MGH Animal Resource Facilities were initially renovated in 1991, with the aid of a $611, 903 Animal Resource Improvement grant. The total project was approximately $3.4 million. The MGH Animal Resource Program was subsequently accredited by AAALAC in July 1993, and continued accreditation was awarded in July 1996. It is important that the Hospital's animal resource program continue in compliance with applicable policies and regulations and that it maintain AAALAC accreditation. Approval and funding of this proposal is essential if MGH is to accomplish this goal and be responsive to the extremely successful research programs at this institution.